Karen L. Sutton

Inductively coupled plasma mass spectrometric detection for chromatography and capillary electrophoresis

Inductively coupled plasma mass spectrometry (ICP-MS) is now a well established detection technique for liquid chromatography, gas chromatography, supercritical fluid chromatography and capillary electrophoresis. A review of the literature with particular regard to ICP-MS as a chromatographic and capillary electrophoretic detector is presented. The various modes of chromatography and capillary electrophoresis are discussed and practical descriptions for hyphenating the techniques with the ICP mass spectrometer are given. Sample introduction systems and data acquisition methods are reviewed along with the numerous applications of ICP-MS as a chromatographic detector. In addition, alternative plasma sources, such as the atmospheric and reduced pressure helium microwave-induced plasmas for chromatographic detection are described.

Development of new SPME fibers by sol–gel technology for SPME-HPLC determination of organometals

Solid-phase micro-extraction (SPME), has advantages of simplicity, low cost, ease of use and rapid pre-concentration and extraction compared to other sample preparation techniques. The technique has found limited use in high performance liquid chromatographic applications because of the unavailability of fibers that are stable and durable in strong organic solvents. This study describes the preparation of fibers that are stable in strong organic solvents (xylene and methylene chloride) as well as acidic and basic solutions (pH 0.3 and 13) using the sol–gel process. The hydrolytic stability of these sol–gel-prepared SPME fibers towards organic solvents and high and low pH solutions can be attributed to the fact that the coating is chemically bonded to the surface of the fused silica substrate. These fibers have been subsequently used to extract organo-arsenic, organo-mercury and organo-tin compounds from aqueous solutions followed by separation using HPLC with UV absorbance detection. Under experimental conditions used, detection limits of 80, 412 and 647 μgl−1for triphenylarsine (Ph3As), diphenylmercury (Ph2Hg) and trimethylphenyltin (TMPhT), respectively, were obtained after extraction and HPLC separation. While these detection limits were comparable and/or slightly better than those obtained using commercial SPME fibers, the thinner coatings (resulting in faster extraction time) and the hydrolytic stability of the sol–gel fibers, towards strong organic solvents and high and low pH solutions, gave them superior characteristics when compared to commercially available fibers.

Speciation of arsenic in fish tissue using microwave-assisted extraction followed by HPLC-ICP-MS

The use of microwave-assisted extraction for the extraction of arsenic species from fish tissue is described. Quantitative extraction of arsenic from spiny dogfish muscle (CRM, DORM-2) was achieved using methanol-water (80+20, v/v) with microwave heating at 65 °C in a closed-vessel microwave system. Extractions were performed with a variety of solvents including water, two different methanol-water mixtures, and a 5% tetramethylammonium hydroxide solution. Extracted arsenic species were separated using both ion-exchange and ion-pair chromatography with ICP-MS detection. The DORM-2 along with three different varieties of fish purchased from a local market were analyzed for arsenic. In all samples, the majority of arsenic present was in the form of arsenobetaine, a non-toxic arsenic species.

Slurry Nebulization in Plasmas

SUMMARY OF CONTENTS Introduction Plasma Techniques Used in Slurry Analysis Importance of Slurry Particle Size on Analytical Performance Slurry Preparation Grinding Methods Dispersion of Slurries Magnetic Stirring and Vortex Mixing Ultrasonic Agitation Solid Particle Size Distribution Measurements Influence of Slurry Concentration Modifications to the Sample Introduction System Nebulizers Spray Chambers Torches Use of a Sheathing Gas Use of a Tandem Source Use of Flow Injection Use of an Inverted Geometry Plasma Calibration Techniques Aqueous Calibration Use of Internal Standards Use of Standard Additions Use of Empirical Correction Factors Use of Intrinsic Internal Standardization Use of Standard Slurries Optimization Use of Mixed Gas Plasmas Matrix Effects Fundamental Studies Aerosol Formation, Transportation and Loss Temperature Measurements Applications of Slurry Sample Nebulization into Plasmas References

Electrochemical control of solid phase micro-extraction using unique conducting polymer coated fibers

The use of a solid phase micro-extraction (SPME) method with poly(3-methylthiophene) coated platinum micro-fiber electrodes to extract arsenate ions from aqueous solutions without derivatization is described. The fibers were fabricated by cycling the working electrode between –0.20 and +1.7 V (vs. Ag/AgCl) in an acetonitrile solution containing 50 mM 3-methylthiophene monomer and 75 mM tetrabutylammonium tetrafluoroborate (TBATFB) electrolyte. All electrochemical procedures (extraction and expulsion) were conducted in a three-electrode system. After fabrication, the conducting polymer film was immersed in the sample solution and converted to its oxidized, positively charged form by applying a constant potential of +1.2 V with respect to Ag/AgCl reference electrode. Arsenate ions migrated into the film to maintain electroneutrality. Upon subsequent reversal of the potential to –0.60 V vs. Ag/AgCl, the polymer film was converted to its reduced, neutral form and the arsenate ions were expelled into a smaller volume (200 µL) of de-ionized water for analysis using flow injection with inductively coupled plasma mass spectrometric (ICP-MS) detection.

ReviewLiquid chromatography–inductively coupled plasma mass spectrometry

The technique of coupling liquid chromatography to inductively plasma mass spectrometry (ICP-MS) is reviewed. A brief introduction to the ICP-MS instrument is given as well as methods to couple the two analytical instruments together. The various types of LC that have been used with ICP-MS detection are discussed and advantages over traditional methods of detection are highlighted, such as the improvements in sensitivity and selectivity. Several applications that have been described in the literature are reviewed. An outlook for the future of LC-ICP-MS, particularly with regard to elemental speciation is given.

Determination of long-lived radionuclides by inductively coupled plasma quadrupole mass spectrometry using different nebulizers

Different nebulizers (cross-flow, ultrasonic and two microconcentric nebulizers) were used for sample introduction of radioactive solutions into a quadrupole-based inductively coupled plasma mass spectrometer (ICP-QMS). The best sensitivity (from 420 to 850 MHz, which is about one order of magnitude higher in comparison with the cross-flow nebulizer) for long-lived radionuclides ( 226 Ra, 230 Th, 237 Np, 238 U and 241 Am) was observed using the ultrasonic nebulizer. However, using the ultrasonic nebulizer, a significantly higher sample size (26-fold) in comparison with the micronebulizers is required. Sample introduction by micronebulization with a small sample size in the low picogram range is the method of choice for the determination of long-lived radionuclides. The precision of determination of a 10 ng l –1 concentration was in the low-% range (and sub-% range) for all measurements using different nebulizer types. The detection limits for the determination of long-lived radionuclides in aqueous solutions applying the different nebulizers were 0.01-0.6 ng l –1 . The flow injection analysis approach was optimized for isotope dilution analysis of 232 Th (using 20 µl of 5 µg l –1 230 Th) by ICP-QMS. The isotopic abundance ratios of 230 Th- 232 Th isotope mixtures ( 230 Th/ 232 Th=0.01, 0.001 and 0.0001) were determined using a microconcentric nebulizer and 1 µg l –1 Th solutions with a relative external standard deviation of long-term stability measurements (over 20 h) of 0.17, 0.62 and 2.66%, respectively.

Ultraviolet absorbance and inductively coupled plasma mass spectrometric detection for capillary electrophoresis—A comparison of detection modes and interface designs

A comparison of ICP-MS and UV absorbance as detectors for capillary electrophoresis (CE) was performed. A high efficiency nebulizer (HEN) with cyclone spray chamber was found to yield detection limits in the low parts-per-billion range while UV detection gave detection limits in the parts-per-million range for the same separation of the lanthanides. Electrokinetic and hydrostatic methods of injection were employed, and it was found that both methods gave similar detection limits and precision values for the separation, for both methods of detection. The use of a traditional concentric nebulizer as part of the CE–ICP-MS interface was evaluated and compared with the HEN. The optimum make-up buffer liquid flow rate was evaluated for the concentric nebulizer and detection limits for the lanthanide separation were calculated. Detection limits with the concentric nebulizer were not improved compared with UV detection, illustrating that the choice of nebulizer for the interface is of primary importance for improved analytical sensitivity. Attempts to use an oscillating capillary nebulizer as part of a CE–ICP-MS interface are also described.

A comparison of capillary electrophoresis using indirect UV absorbance and ICP-MS detection with a self-aspirating nebulizer interface

A comparison of capillary electrophoresis (CE) migration times using standard on-column UV detection and inductively coupled plasma mass spectrometry (ICP-MS) is presented for two different CE separations. The first is a separation of five arsenic compounds, four anionic species and one neutral, using reverse polarity in a chromate buffer with an electroosmotic flow modifier. The second CE separation employs normal polarity for the separation of eleven lanthanide cations using a hydroxyisobutyric acid (HIBA) buffer with an indirect UV detection reagent. The CE-ICP-MS interface is based on a tee design which introduces a sheath flow around the CE capillary using a self-aspirating make-up electrolyte with a microconcentric nebulizer (MCN-100). Migration times observed for CE-ICP-MS electropherograms are comparable to migration times acquired with UV detection, and may be adjusted by changes in the make-up liquid level position. The precision of peak areas (<2%) and migration times (<4%) obtained using CE-ICP-MS is comparable to that obtained using online UV absorbance detection. CE-ICP-MS limits of detection are in the low ng ml−1 range for the analytes studied.

Comparison of four nebulizer–spray chamber interfaces for the high-performance liquid chromatographic separation of arsenic compounds using inductively coupled plasma mass spectrometric detection

Four nebulizer-spray chamber combinations were used and evaluated as interfaces for HPLC with ICP-MS detection. The oscillating capillary nebulizer (OCN), the concentric nebulizer and the Meinhard high-efficiency nebulizer (HEN) were used with single pass, double pass and cyclonic spray chambers. Monomethylarsonic acid, dimethylarsinic acid, arsenobetaine and arsenocholine were separated using an ion-pair liquid chromatographic method on a C 18 column. A calibration curve, limits of detection, precision for five injections, peak efficiency and peak asymmetry were calculated for each compound using each nebulizer-spray chamber combination. The HEN with cyclonic spray chamber displayed the lowest detection limits (1.0-2.3 μg l -1 for the four arsenic compounds) and had the lowest precision of duplicate injections (RSD as high as 14%). The concentric nebulizer had reasonably low detection limits; the standard nebulizer had lower detection limits (1.6-3.6 μg l -1 ) than the cyclonic spray chamber (4.5-11 μg l -1 ). The OCN had the highest detection limits under chromatographic conditions identical with those for the other interfaces (160-360 μg l -1 ). The precision (RSD) of duplicate injections for the concentric nebulizer and the OCN ranged from 2.1 to 8.6%.